1. Field of the Invention
The present invention relates to a stamper-forming thin film used to form a stamper which is a mold for mass production of optical disks such as compact disks (CDs) and digital versatile disks (DVDs), and to a stamper-forming electrode material for making the stamper-forming thin film. More particularly, the invention is directed to a stamper-forming thin film used as an electrode for forming the stamper by electroforming, and to a stamper-forming electrode material for making the electrode. The invention also relates to a method of manufacturing optical disks such as CDs or DVDs using the stamper.
2. Description of Related Art
To manufacture optical disks such as CDs or DVDs by a prior art technique, first, as shown in FIG. 3A, a resist film 102 is formed by spin coating or the like on a polished, smooth and flat surface of a supporting plate 101 made of glass. Then, this resist film 102 is patterned. For the patterning, as shown in FIG. 3B, the resist film 102 is exposed to a laser beam to form a latent image 102a, which is thereafter developed. As a result, a pattern 102b of grooves, or otherwise referred to as a grooved pattern 102b, is formed in the surface of the resist film 102, as shown in FIG. 3C.
After the patterning, as shown in FIG. 3D, an electrode film 103 made of a metallic material is deposited on the resist film 102 by sputtering, evaporation, or the like in a manner applying a coating over the entire part of the grooved pattern 102b. The electrode film 103 is made of a single metallic material, nickel (Ni), which is highly conductive and hard to change in composition after film formation, into a uniform thickness. Thereafter, as shown in FIG. 3E, a Ni metallic layer 104 is stacked on the electrode film 103 by electroforming using the film 103 as an electrode.
Then, as shown in FIG. 3F, the metallic layer 104 is separated, together with the electrode film 103, from the surface of the resist film 102 to produce a stamper 104a which is a monolithic member consisting of the electrode film 103 and the metallic layer 104. A surface of the stamper 104a has a pattern 104b of projections, or otherwise referred to as a projected pattern 104b, which has been transferred as the inverse of the grooved pattern 102b. Then, a synthetic resin material is injected into the stamper 104a as a mold toward its projected pattern 104b, to form a substrate on which a grooved pattern exactly identical with the grooved pattern 102b has been copied. Thereafter, a reflector film, a protective layer, etc. are stacked on the substrate in a manner coating the copied grooved pattern, to complete the manufacture of an optical disk.
By the way, latest versions of optical disks are required to have a greater recording density per unit area in order to increase their storage capacity without increasing their size, as in DVDs versus CDs, for example. To meet this requirement, an electron beam is replacing a laser beam during the patterning to implement a narrower groove width, for formation of a higher-definition grooved pattern 102b. For electron-beam exposure, electron-attracting elements such as chlorine, sulphur and fluorine, groups having an electron-attracting function (electron-attracting groups) or the like are added to a resist material for forming the resist film 102b, to provide the resist film 102b with improved electron absorption sensitivity.
However, the use of the resist film 102 with improved electron absorption sensitivity may cause damage, such as deterioration, to the electrode film 103 during electroforming for stacking the metallic layer 104 on the electrode film 103, due to Ni in the electrode film 103 reacting with the electron-attracting elements or groups. Since the surface of the projected pattern 104b of the stamper 104a is formed of the electrode film 103, the damaged electrode film 103 roughens the surface of the projected pattern 104b of the stamper 104a. Thus, such a stamper 104a cannot transfer the grooved pattern 102b to the substrate accurately, resulting in replication of low-performance optical disks with low signal-to-noise ratio (SNR) due to greater noise during data reading.